<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    #d1{
      width: 100px;
      height: 100px;
      border: 5px solid blue;
      /*绝对定位*/
      position: absolute;
      top: 50px;
      left: 50px;
    }

    #d2{
      width: 100px;
      height: 100px;
      border: 5px solid red;
    }
    #d3{
      width: 100px;
      height: 100px;
      border: 5px solid yellow;
    }

    #big{
      width: 100px;
      height: 100px;
      border: 5px solid green;
      background-color: green;

      /*!*先将父级元素设置为相对定位*!*/
      position: relative;
    }

    #big>div{
      width: 50px;
      height: 50px;
      background-color: deeppink;
      /*绝对定位*/
      position: absolute;
      top: 10px;
      left: 10px;
    }


  </style>

</head>
<body>

  <div id="d1">div1</div>
  <div id="d2">div2</div>
  <div id="d3">div3</div>

  <div id="big">
    <div></div>
  </div>

</body>
</html>